Coating method with cleaning

ABSTRACT

An apparatus and method are provided for producing a coating of resinous material upon only a portion of a workpiece, the resinous material preferably being deposited upon the workpiece as electrostatically charged solid particles. One zone of the workpiece is contacted, in the substantial absence of relative movement therebetween, with the cellular, resiliently deformable contact surface of a particle removal member to pick up particles of the resinous material therefrom without wiping or brushing the surface. Preferably, the resinous material is of such a nature that it can be fused to a unified coating, and the apparatus and method are particularly adapted for producing thermoplastic coatings upon armature rotors for electric motors.

O United States Patent 11 1 1111 3,889,015

English June 10, 1975 [54] COATING METHOD WITH CLEANING 3,660,136 5/1972Guilbault et a1. 117/17 3,703,157 11/1972 Maksymiak et al.... 118/D1G. 5[751 Inventor: w'mam Engllsh Bndgeport, 3,807,853 4/1974 Hudson 355/15Conn.

[73] Assignee: Electrostatic Equipment Primary ExaminerMichaelSofocleous Corporation, New Haven, Conn. 22 Filed: May 24, 1972 7]ABSTRACT [21] Appl 256 294 An apparatus and method are provided forproducing a coating of resinous material upon only a portion of aworkpiece, the resinous material preferably being de- U-S. Cl. positedupon the workpiece as electrostatically l18/ /6; 427/ charged solidparticles. One zone of the workpiece is [51] Int. 844d contacted in theubstantial absence of relative move. Field of Search 21, menttherebetween, with the cellular, resiliently de- 1 134/6 formablecontact surface of a particle removal memher to pick up particles of theresinous material therel References Cited from without wiping orbrushing the surface. Prefera- UNITED STATES PATENTS bly, the resinousmaterial is of such a nature that it 2,862,646 12 1958 Hayford et al222/193 can be fused a unified Coating, and the PP K 2,894,744 7/1959SChUlZC 271 51 and method are Pamcularly adapted for P g 2,997,7768/1961 Matter et a1. l17/DIG, 6 thermoplastic coatings upon armaturerotors for elec- 3,lO2,043 8/1963 Winthrop et al.. 1l7/DIG. 6 tricmotors. 3,247,004 4/1966 Dosser 117 19 3,261,707 7/1966 Korski et a1.117/18 7 Clams, 17 Drawmg Flgllres POWDER RECOVERY AND F'EED POWDERREPLENISH 0 ELECTRIC INTERFACE /ACCESS CHANNEL L r o/mm PROCESS UNITOVEN U N T T MAIN i i CONTROL PATENTEUJUH 10 ms SHEET u m w mw :zJmmuwomm 02560 PATENTEDJUN 10 1975 SHEET PATENTEUJUN 10 m5 3 8 89,015

' SHEET 4 FIG. 8

PATENTEDJUH 10 I975 SHEET I88 FIG. 12 M 1 O TL. 200

COATING METHOD WITH CLEANING BACKGROUND OF THE INVENTION Of the variousways in which coatings of fusible resinous materials are produced uponvarious workpieces, those in which the material is applied inparticulate or powdered form are often found to be the most effectiveand satisfactory. Such techniques are used to produce coatings upon awide variety of workpieces, including continuous lengths of wire andstrip stock as well as individual objects which are often of a complexconfiguration, as would make coating by other techniques difficult orimpossible. For example, attempts have been made to insulate the slotsof rotors and stators for electric motors by depositing the resin inpowdered form, which has proven particularly difficult due to thepresence of reentrant surfaces which must be covered.

A common method of producing coatings of thermoplastic particulatematerials is to utilize heat from the workpiece to cause softening andfusion of the particles upon contact. Thus, it has long been thepractice to heat the article and to then submerge it in a bed (desirably fluidized) of the particulate material so as to produce a coatingupon all exposed surfaces, and as far as is known prior attempts toproduce coatings from powdered resins upon electric motor componentshave employed this technique. However, the inherent drawbacks are quiteapparent, and include the need for masking of portions of the workpiecewhich are to remain free from the coating material and/or the need tohandle or direct the resin in such a manner that contact will beavoided. Not only are such precautions timeconsuming, but frequentlythey are difficult if not impossible to achieve in practice. Moreover,since the amount of material deposited using such a method is dependentupon the intensity of heat available from the workpiece and/or theduration of exposure, uniform thicknesses are oftentimes most difficultto obtain.

It is also well known that electrostatic forces may be utilized to causeattraction and adhesion of particles of resinous materials to a widerange of workpieces, which may thereafter be heated or otherwise treatedto fuse the resin and produce the final unified coating. This approachhas many advantages including uniformity of coverage, ease of access toundercut or reentrant surfaces, coating thickness control, etc.Nevertheless, the production of preferential deposits upon selectedareas of the object has typically relied upon the use of mechanical orair masking techniques which are not entirely satisfactory under certaincircumstances, such as when it is necessary to obtain a virtually cleansurface closely adjacent to one that is to be relatively thicklycovered.

Accordingly, it is an object of the present invention to provide a novelmethod and apparatus for the production of a coating of a solid,particulate resin upon a limited portion of a workpiece.

A more specific object of the invention is to provide such a method andapparatus for electrostatically coating the workpiece and for effectingthe removal of the resinous material from selected portions thereofwhich are to be uncoated.

An even more specific object is to provide such a method and apparatuswhereby a generally cylindrical article having reentrant surfaceportions may be coated with an adherent deposit upon the reentrantsurface portions thereof.

Another object of the invention is to provide such a method andapparatus whereby such coatings may be produced quickly, easily andeconomically, which method and apparatus may be automatic andcontinuous.

A further object is to provide a novel contact belt unit which isadapted to remove the particulate resin from one zone of a workpiecewithout causing undue thinning or thickening of the deposit on anadjacent zone thereof.

SUMMARY OF THE DISCLOSURE It has now been found that certain of theforegoing and related objects are readily attained in apparatuscomprising, in combination, a chassis, particle removing means thereon,means for carrying a workpiece along a travel path, and drive means forthe particle removing means and carrying means. The particle removingmeans includes a member movably mounted over the travel path and havinga relatively resiliently deformable contact surface thereon of smallopen-cell construction, which is disposed for direct contact upon aportion of the workpiece as it is carried along the travel path. Thecarrying means and particle removing means are adapted for coaction tomove the contact surface and'the contacted portion of the workpiece atthe same linear speed during contact to substantially prevent wiping ofthe workpiece by the contact surface.

Preferably, the portion of the travel path over which .the particleremoving means is mounted is generally rectilinear, with the member ofthe particle removing means being positioned to move in a circuitouspath in a plane parallel to the axis of the travel path portion. Theparticle removing means may comprise a set of spaced pulleys about whichextends an endless flexible belt having the contact surface disposed onits outer surface. Most desirably, the contact surface is comprised ofan open-cell foam elastomer having a cell size of about 1 to 20 mils,and polyurethane is advantageously utilized as the elastomer.

The particle removing means may include a plurality of contact elementsspaced along the travel path to sequentially contact substantially thesame portion of the workpiece. Alternatively, or additionally, theparticle removing means may include a plurality of elements which arespaced across the travel path to contact different portions of theworkpiece.

In the preferred embodiments of the invention, the apparatus is adaptedfor the coating of a generally cylindrical article, and the carryingmeans thereof is a conveyor adapted to support the article with its axisextending transversely across the travel path. In such an embodiment,the conveyor desirably supports the article for free rotation thereonwith contact of the article by the contact surface of the particleremoving means causing rotation thereof as the conveyor carries thearticle along the travel path. The apparatus is especially suited forthe coating of an armature rotor having a cylindrical core portion witha shaft portion extending axially from each end thereof. In such a case,the conveyor is adapted to engage the shaft portions of the rotor, andthe contact surface of the particle removing means is disposed forcontact with the circumferential surface of the core portion so as toeffect the removal of particles therefrom.

The apparatus may include vacuum means disposed adjacent the contactsurface to effect the removal of particles of the resinous materialtherefrom. In instances in which the apparatus is adapted for the production of a coating of a thermoplastic resinous material, it willadditionally include heating means on the chassis along the travel pathdownstream of the particle cleaning means. Such heating means will beadapted to heat at least a first zone of the workpiece to produce atleast partial fusion and coherence of the particles thereon. Moreover,the apparatus may include means on the chassis upstream of the particleremoving means for producing a cloud of electrostatically charged solidparticles of resinous material.

In especially preferred embodiments of the invention the cloud producingmeans employed in the apparatus includes an electrostatic cloud chamber.Such a chamber may comprise a receptacle having means for producing afluidized bed of charged particles including a gas-permeable plateextending thereacross in a generally horizontal intermediate plane andspaced above the bottom wall of the receptacle to define a plenumchamber therebelow. The receptacle also has electrode means extendingthereacross to electrostatically charge particles of solid resinousmaterial passing proximate thereto. Most desirably, the apparatus willinclude a particulate material reservoir having feed means communicatingwith the cloud chamber. In such a case, the electrode means may span alesser area than the gaspermeable plate to provide an electrode-freevertical corridor within the receptacle through which particles of theresinous material may pass without acquiring a significant charge. Adevice for sensing the level of the bed of particles within thereceptacle, in response to which the feed means conveys resinousmaterial from the reservoir to the chamber when the bed level fallsbelow a preselected height, may also be provided. The sensing device ispositioned within the vertical corridor over the horizontal porousplate, to thereby minimize the effect of electrostatic charging upon thesensed level of the bed. The electrode employed may be a generallyplanar, grid-like structure disposed adjacent the upper surface of thegas-permeable plate, and electrode and plate may be substantiallycoextensive except at one area of the plate over which the electrodedoes not extend, thereby providing the electrode-free vertical corridor.

Certain objects of the invention are attained in accordance with themethod hereof, whereby a cloud of electrostatically charged solidparticles of resinous material is produced and the workpiece is exposedto the charged particles with a charge effectively opposite thereto, soas to cause a layer of particles to deposit thereon. Thereafter, aportion of the workpiece is contacted with a relatively resilientlydeformable contact surface having a small open-cell construction. Suchcontact is effected under conditions avoiding relative movement betweenelements of the workpiece portion and of the contact surface while insuch contact, to avoid wiping action from occurring therebetween. Thecontact surface and workpiece are thereafter separated with theparticles lodged within the cells of the contact surface to therebyeffect the removal of particles from the contacted portion.

Preferably, the workpiece moves along a travel path during contact withthe contact surface, which simultaneously moves adjacent thereto. Theworkpiece may be generally generally cylindrical article supported forfree rotation about its axis transversely across the travel path.Contact by the contact surface on a circumferential surface of thearticle causes rotation thereof with the circumferential surface movingat the same linear speed as that at which the contact surface moves. Itis especially preferred that the article he an armature rotor for anelectric motor having reentrant surface portions in the cylindrical coreportion thereof defining winding slots therein. In such an instance, thecontact element removes particles from the circumferential surface ofthe core portion without causing undue thinning or thickening of thelayer of particles along the edges of the slots. Most desirably, thecontact surface is comprised of an open-cell foamed elastomer having acell size of about 1 to 20 mils, and the resinous material is a powderconsisting essentially of particles smaller than about mesh. Theresinous material may be thermoplastic, in which event the method willinclude the additional step of heating the particles of resinousmaterial remaining on the workpiece subsequent to the particle removalstep, so as to cause at least partial fusion and coherence thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of apparatusembodying the present invention;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a side elevational view of the coating process unit of theapparatus of FIGS. 1 and 2, drawn to an enlarged scale and with housingportions removed to expose internal features thereof;

FIG. 4 is a perspective view of an armature rotor for which theillustrated apparatus is particularly adapted;

FIG. 5 is a fragmentary perspective view of the forward end of thecoating process unit including the load zone and a portion of theelectrostatic coating station, drawn to a scale enlarged from that ofFIG. 3;

FIG. 6 is an enlarged sectional view along line 66 of FIG. 3illustrating the support and positional control structure provided atthe load zone and showing an armature rotor carried on the forwardconveyor for movement therethrough;

FIG. 7 is an end view of the electrostatic coating station along line7-7 in FIG. 3 with portions of the housings broken away to illustratethe internal features thereof and drawn to a greatly enlarged scale;

FIG. 8 is a side elevational view of the sensing device employed in thecloud-coating unit of the electrostatic coating station;

FIG. 9 is a fragmentary end view along line 99 in FIG. 3 showing thepowder removal zone of the apparatus with the contact belt unit thereofin its normal operating position, drawn to a greatly enlarged scale andhaving portions in vertical section to illustrate the constructionthereof;

FIG. 10 is a front view of the powder removal zone at an acute angle tothe upper surface of the deck, drawn to a slightly diminished scale fromthat of FIG. 9 and showing the contact belt unit in its raised position;

FIG. 11 is a fragmentary end view of the powder removal Zone along lineIl-1l of FIG. 3, drawn to the scale of FIG. 9;

FIG. 12 is a fragmentary plan view of the shaft cleaning units providedwithin the powder removal zone, drawn to a scale enlarged from that ofFIG. 10 and with the hold-down brackets removed to expose the vacuumslots thereof;

FIG. 13 is a side elevational view of the vacuum nozzle and associatedparts employed with each of the units of FIG. 12;

FIG. 14 is an enlarged sectional view along line 14-14 in FIG. 3 showingthe precuring unit of the apparatus with an armature rotor passingtherethrough, and in phantom line showing the raised position of thecover assembly;

FIG. 15 is a perspective view of the air knife assembly at the powderrecovery zone of FIG. 3, drawn to a greatly enlarged scale;

FIG. 16 is a fragmentary perspective view to a greatly enlarged scale ofthe intermediate conveyor employed in the apparatus; and

FIG. 17 is a fragmentary perspective view of one band of the endmostconveyor of the apparatus, drawn to the scale of FIG. 16.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Turning now in detailto the appended drawings, therein illustrated is an armatureslot-coating system embodying the present invention and details of thevarious units and zones thereof. FIGS. 1 and 2 illustrate the overalllayout of the system, the heart of which is the coating process unit, sodesignated on the drawing. Auxiliary to the coating process unit is anoven and a cooling unit, and main control and oven control facilitiesare furnished. Also included in the system to enable a desirable mode ofoperation is a power recovery and feed unit and a powder replenishmentunit. As will be appreciated from FIG. 2, the workpieces are loaded atan infeed zone at the left-hand end of the coating process unit fromwhich they pass serially through an electrostatic coating zone, a powderremoval zone, a precure zone, and a powder recovery zone; they then passinto the oven and finally through the coolingunit. Excess powder fromthe electrostatic coating zone is recovered in the powder recovery andfeed unit and is returned through an appropriate conduit to the coatingunit on a substantially continuous basis, and additional powder isfurnished from the powder replenishing unit as needed. An electricinterface access channel runs along the rear of the coating process unitto provide power at the various zones thereof.

With specific reference now to FIG. 3, the coating process unit of thesystem is depicted in greater detail. It includes a frame 10 on whichare rotatably supported three conveyor drive sprockets, generallydesignated by the numerals ll, 12 and 13 respectively from left to rightin the Figure, and idler wheels 14 are positioned between adjacentsprockets. A forward endless conveyor, generally designated by thenumeral 16, runs about sprockets 1 1 and 12 and the idler wheel 14therebetween; a center endless conveyor, which is generally designated18, runs about sprockets 12 and 13 and about the idler wheel 14positioned between them, and a rearward endless conveyor, which isgenerally designated 20 and is fragmentarily illustrated, runs about theright-hand sprocket 13 and a cooperating sprocket which is notillustrated and is positioned adjacent the end of the cooling unit shownin FIGS. 1 and 2. A drive pulley 22 operates the powder removal unit andis driven by the electric motor 24 which is supported within the frame10. A second motor 25 is connected to sprocket 13, thereby synchronouslydriving all conveyors 16, 18, 20 since they are coupled by the sprockets12, 13.

Although the invention is not to be construed as limited to coating ofany particular workpiece, and may be 5 feasible for coating selectedportions of objects which are elongated or of continuous length, thesystem illustrated is especially suited for the coating of armaturerotors of the type generally designated by the numeral 26 in FIG. 4, andis intended principally for that purpose. The rotor 26 is ofconventional configuration and includes a cylindrical core portion 28having spaced about its circumference four axially extending, reentrantwinding slots 30. Extending from opposite ends of the core portion 28are simple and crank-type shafts 32, 34 respectively, and the shaft 34has a spring clip 35 engaged upon it adjacent the end of the coreportion As will be appreciated, the slots of the rotor 26 are designedto receive wire windings, making it necessary to provide the slots 30and the opposite end faces 37 of the core portion 28 with a layer ofinsulating material to enable magnetic poles to be defined thereon. Itis also important that the outer circumferential surface of the coreportion 28 and the shafts 32, 34 be free from insulating material; thepresent system is unique in enabling the rapid and facile production ofcoated rotors having deposits of insulating material which are presentonly at selected locations and are of substantially uniform thickness,particularly along the edges of the slots 30.

FIG. 5 illustrates in greater detail the loading zone of the coatingprocess unit, whereat a narrow rectangular opening 38 is providedthrough the deck 36 of the frame 10 to accommodate the edge of drivesprocket 11. As can be seen, the forward conveyor 16 is comprised of twoindependent flexible and continuous parallel bands, generally designatedby the numerals 44 and 45, and the drive sprocket 11 consists of a pairof parallel sprocket wheels 40 mounted on a common shaft for concurrentrotation. Each of the sprocket wheels 40 has about its circumferentialedge a multiplicity of small rectangular teeth 42; the belt portion 46of each of the bands 44, is provided with a multiplicity of rectangularapertures 48 which are spaced along the length thereof, the apertures 48meshing with the rectangular teeth 42 of. the respective sprocket wheels40 as the bands pass thereover along their travel path. Extending at aright angle from the inner edge of the belt portion 46 of each of thebands 44, 45 are a multiplicity of carrier tabs 50, 50' respectively,and each tab 50, 50 has bevelled shoulders 51 leading into the shaftslots 52, 52' therebetween. As will be appreciated, the slots 52, 52'are dimensioned to receive the shafts of the armature rotor 26, and thetabs 50' are slightly narrower than the tabs 50 to render the slots 52'somewhat wider than the slots 52, thereby enabling close-fittingengagement of shafts 32, 34, notwithstanding their different diameters.It will be evident that the bevelled shoulders 51 facilitate insertionand removal of the shafts of the armature rotors 26 into and from theslots 52.

As can most readily be seen by additional reference to FIG. 6, one of apair of elongated rectangular curb blocks 54 extends along each side ofthe upper flight of the conveyor 16, with the curb blocks 54 beingsecured to the deck 36 by bolts 56 (fastened in an appropriate manner,not illustrated). Coextensive with each of the curb blocks 54 is a guiderail 58 which is secured upon the upper surface of the associated curbblock 54 by a number of bolts 60 spaced along the length thereof. Ashallow recess 61 is provided along the upper surface adjacent the inneredge of each of the curb blocks 54 enabling the belt portion 46 of theconveyor bands 44, 45 to pass between the curb blocks 54 and the bottomsurface of the guide rails 58. The guide rails 58 have inner surfaceswhich extend downwardly and then at an angle inwardly to provide guidesurfaces 62 sloping downwardly toward the travel path. The guidesurfaces 62 define therebetween a trough which is dimensioned so thatarmature rotors 26 carried by the conveyor 16 extend thereacross withlittle free space adjacent the ends, thus ensuring that the rotors 26remain accurately positioned across the conveyor 16 and centrallypositioned on the axis of the travel path of the unit.

Extending forwardly from adjacent the ends of the curb blocks 54 is asupport extension 64 which underlies the conveyor 16 and providessupport therefor as the bands 44, 45 disengage from the sprocket wheels40. Supported above the extension 64 is a loading platform portion 66from which extend rearwardly a pair of thin support rails 68 which aresecured in a parallel relationship against the inner faces of the curbblocks 54. The loading platform 66 is provided to facilitate loading andseating of the rotors 26 in the slots 52 of the conveyor 16, and thesupport rails 68 provide underlying support for the shafts 32, 34 as therotors 26 proceed along the travel path, it being appreciated that theshafts ride upon the upper edges of the support rails 68 rather thanresting at the bottom of the slots 52. As a result, the conveyor 16serves only to drive the rotors 26 forwardly through the system, withcontact upon the rails 68 causing them to rotate as they are conveyed.

From the load zone, the armature rotors 26 are conveyed to theelectrostatic coating station illustrated in detail in FIG. 7, which iscomprised of a hood, a powder feed stack, and an electrostatic coatingchamber, generally designated by the numerals 72, 74 and 76respectively. The electrostatic coating chamber 76 consists of anupwardly opening enclosure 78 secured against the bottom surface of thedeck 36 and having a bottom wall opening through which air is chargedfrom a pressurized source 79 thereof. A horizontal porous ceramicpartition 80 divides the enclosure 78 into a lower air plenum chamber 82and an upper cloud chamber 84. The partition 80 supports an overlyinggrid-type electrode 86 connected to a diagrammatically illustrated highvoltage source 88 and extending partially across the enclosure 78 toprovide an electrodefree area 85 between its inner edge 87 and thesidewall 89, through which extends an imaginary vertical corridor.

Within the corridor, supported upon the depending bracket 92, is apneumatically operated fluidic sensing device comprised (as seen in FIG.8) of a body 90 with a wire actuating finger 94 extending therefrom; oneappropriate device is sold by Norgren Fluidics of Littleton, Colo. underthe name FEATHERFLEX SFS-OIO- 000. On the outer end of the wire finger94 is a float sphere 96 which may be fabricated of a foamed polystyreneor comparable lightweight material, and pneumatic control lines 98extend from the body 90 and are connected to control means (notillustrated).

The feed stack 74 consists of a sifter box 100 having a screen 102horizontally positioned across the central portion 'LllLI'EOf and havinga recycle feed conduit 104 and a ,plenish conduit 106 leading thereinto.As will be appreciated, the conduit 104 extends from the powder recoveryand feed unit and the conduit 106 extends from the powder replenishmentunit, both shown in FIGS. 1 and 2. The conduits 104, 106 deliverthermoplastic resin powder 103 into the upper portion of the sifter boxfrom which it passes through the screen 102 and the opening 108 in thedeck 36 with lumps and foreign matter being removed by the screen 102.The powder 103 then falls upon the porous partition 80 where it becomesfluidized by air passing upwardly from the plenum chamber 82 in aconventional manner. The fluidized powder 103 exerts an upward forceupon the float sphere 96 of the fluidic sensing device; when thequantity of powder 103 above the partition 80 is insufficient to urgethe sphere 96 (and hence the actuating finger 94) upwardly to thenecessary extent, a signal from the sensor causes the control means (notillustrated) to deliver an additional quantity of powder 103 through theconduit 106 from the powder replenish unit, thereby correcting thedeficiency.

The hood 72'is positioned over an elongated slot 1 10 in the deck 36along which the parallel guide rails 68 extend. It is secured to thedeck by bolts 112 and has a tunnel portion 114 with an end wall 116forming a partial closure therefor and defining a tunnel opening at eachend thereof. A stack portion 118 extends upwardly from the tunnelportion 114 of the hood 72, and has a takeoff conduit 120 which isattached to a suitable vacuum source and enables excess powder to beremoved from the coating station. Such powder is returned to therecovery and feed unit for ultimate recycle through the conduit 104leading to the feed stack 74. An elongated baffle plate 122 is inclineddownwardly from each sidewall of the tunnel portion 1 14 toward thetravel path of the unit, and the plates 122 cooperate with the carriertabs 50, 50' to confine powder 103 which passes upwardly through theslot 110 to the central portion of the rotors 26 passing thereover.

As will be appreciated, the powder 103 employed for the coatingoperation is of such a nature that it is capable of acquiring anelectrostatic charge as the particles pass through the grid electrode86. The rotors 26 are maintained at ground potential (such as bygrounding the conveyor 17 with which they are in contact) during passageover the slot 110, thus causing attraction and adherence of chargedpowder particles to the surfaces of the rotors 26, with theelectrostatic effect ensuring that all exposed surfaces, includingwinding slots 30, are coated. Due to the charge on the powder particles,it is important that the fluidic sensing device be positioned over theelectrode-free area 85 of the horizontal partition 80. In this regioncharging of particles is minimized, as a result of which the attractiveforce from the grounded rotors 26 is quite insignificant and particlesthereat are elevated only by the buoyant effect of the pressurized air.Otherwise, the electrostatic force on the particles would lead to aninaccurate indication of the quantity of powder present in the system,rendering control of the automatic replenishment system virtuallyineffective.

Since the armature rotors 26 must be substantially free of insulatingmaterial on the circumferential surface of the core portion 28 and alongthe shafts 32, 34, and since in the coating step powder deposits uponall exposed surfaces, the method and apparatus of the invention requirethat means be provided for removing powder from selected surfaces of therotor 26 where it is unwanted. To that end, the illustrated apparatus isprovided with a powder removal station which includes the contact beltunit, generally designated by the numeral 124, and shown in FIGS. 3, 9and 10. The contact belt unit 124 includes an elongated forward framemember 126 from which extend rearwardly triangular mounting brackets 128which are pivotally supported upon posts 130 projecting upwardly fromthe deck 36. In this manner, the unit 124 is hingedly supported forready displacement from the position over the deck 36 shown in FIG. 9 toits open position in FIG. 10. Affixed in a central location behind theforward frame member 126 is a pinion block 131 which, in turn, has agear train block 132 mounted behind it. A short central shaft 134 isjournaled at its ends by appropriate means to extend transverselythrough the forward frame member 126, the pinion block 131, and the geartrain block 132, and it has a drive gear 136 affixed on it within thegear train block 132. The shaft 134 also has a drive pinion 138 affixedto it in front of the gear 136, with the pinion 138 residing generallywithin the pinion block 131. A lower shaft 140 is journaled at its endsand extends transversely between the pinion block 131 and the gear trainblock 132; on it is affixed, in meshing engagement with the drive gear136, an upper transfer gear 142. The transfer gear 142 communicatesthrough a deck opening 143 with a lower transfer gear 144 which issupported upon a shaft 146 positioned and appropriately journaled (bymeans not shown) below the deck 36. As can be seen in FIG. 3, the lowertransfer gear 144 meshingly engages a gear 148 which is affixed to theshaft on which the drive pulley 22 is supported. In this manner, poweris delivered from the motor 24 through the drive pulley 22 and the trainof gears 148, 144, 142 ultimately to the drive gear 136 for the contactbelt unit 124. As can be seen, pivoting the unit 124 upwardly about theposts 130 simply disengages the gears 142 and 144, discontinuingoperation of the unit 124 and permitting access to the normally coveredportion thereunder.

A belt pulley shaft 150 is journaled in the forward frame member 126 andpinion block 131 on either side of the central shaft 134, and a pulleypinion (not exposed but identical to pulley pinions 152 to be discussedhereinafter) is affixed to the inner end of each of the shafts 150 andis in meshing engagement with the drive pinion 138. (It will beunderstood that the pulley pinion on shaft 150 to the left of shaft 134in FIG. lies behind pinion 138, as viewed in FIG. 9, and that thepulleys and belt assembly at the left side of FIG. 9 are shown along asection line somewhat forward of line 9-9.) To the opposite ends of thepulley shafts 150 are affixed belt pulleys 154. Spaced to either side ofthe central pinion block 131 is an auxiliary pinion block 156 in whichis contained a pair of belt pulley shafts 150 and a transfer pinionshaft 134 therebetween. The inner ends of the pulley shafts 150 haveaffixed to them pulley pinions 152 (as can be seen in the left-handauxiliary pinion block 156 in FIG. 10) and the transfer pinion shaft 134has affixed to its inner end a transfer pinion 158 in meshing engagementwith each of the pulley pinions 152 on either side thereof. Adjacenteach end of the forward frame member 126 is a rectangular bearing block162 in which is journaled, by appropriate means, a belt pulley shaft150. A belt pulley 154 of the type previously referred to is secured onthe outer end of each belt pulley shaft supported in either theauxiliary pinion blocks 156 or the bearing blocks 162.

The eight pulleys 154 function as four sets with adjacent pairs ofpulleys supporting a belt assembly consisting of an underlying supportelement 164 and an outwardly exposed contact element 166, backup blocks165 being affixed to the frame member 126 within the confines of eachassembly. The contact element is preferably of a foamed elastomer or acomparable material providing an open-cell outer surface. Such astructure enables the contact element 166 to pick up powder from thesurface of the core portion 28 simply by contact therewith, with nowiping or brushing action being necessary or desirable. Moreparticularly, it is believed that by simple contact of the element 166upon the rotor 26 the powder present on the surface contacted becomeslodged in the cells or small Openings present over the surface of theelement 166, such engagement overcoming the electrostatic attraction andpermitting pick-up of particles by the element 166. Typical of thematerials that are suitable as the contact element 166 are polyurethane(preferably) and silicone resins, polybutadine, butyl and neoprenerubbers, etc. The material should provide open cells of about 1 to 20mils at the surface of the element 166, and accordingly the elastomerfoams are very conveniently used; however, other materials might besubstituted, and it is not believed that the internal structure is ofbasic significance. The support element 164 may be a timing belt (i.e.,having transversely extending ridges about its inner surface) with thepulleys 154 being provided with corresponding ridges and grooves, orsquare teeth, to cooperate therewith. Drive power is transferred fromthe motor 24, through the gears 148, 144, 142, 136, to the pinion 138within the central pinion block 131, and to the innermost belt pulleys154. Due to the interconnection through the pulley pinions 152 andtransfer pinion 158 within each of the auxiliary pinion blocks 156, thebelt assemblies on the outer sets of pulleys 154 are simultaneouslydriven, with all belt assemblies rotating at precisely the same rate andin the same direction.

As is seen in FIG. 9, a central sprocket wheel 40' having rectangularcircumferential teeth 42 is supported on a common shaft (not shown) withtwo outside sprocket wheels 40. The outside wheels 40 correspond to thesprocket wheels bearing the same numeral which constitute drive sprocket11, and the three commonly supported wheels 40, 40 provide theintermediate drive sprocket 12. Endless conveyor 18 has the constructionillustrated in FIG. 16 and passes about the central sprocket wheel 40.The conveyor 18 consists of a central band 176 having carrier tabs 178,178 extending at right angles from the side margins thereof. The tabs178' are slightly narrower than the tabs 178, again to render the slots180 therebetween slightly wider than the slots 180 between the tabs 178to snugly receive the shafts 34, 32 of the rotor 26, respectively. Thefollowing edges of each of the tabs 1'78, 178' have bevelled shoulders51 to faciliate entry of the shafts 32, 34 thereinto; however, it willbe noted that the forward edges of the tabs 178, 178 are not bevelled,and the reason therefor will be explained directly.

As can be seen in FIG. 10 a transfer of the rotors 26 occurs within thepowder removal zone with the rotors 26 shifting from the forwardconveyor 16 to the intermediate conveyor 18. Engagement of bothconveyors l6, 18 on different sprocket wheels 40, 40' of the commondrive sprocket 12 and the construction employed permits conveyor 18 topass between the bands 44, 45 of the conveyor 16. At the point of commontangency of the conveyors 16, 18 to sprocket 12 of the respective slots52, 180 thereof are substantially aligned, causing the shafts 32, 34 ofthe rotors 26 to momentarily reside in slots of both conveyorssimultaneously. As the bands 44, 45 of the forward conveyor 16 passdownwardly about the sprocket 12, the upper corners of the tabs 180, 180of the intermediate conveyor 18 engage behind the shafts 32, 34 tosmoothly and effectively carry them out of the slots 52 with thebevelled shoulders 51 at the following edges of the tabs 50, 50facilitating withdrawal. Thereafter, the rotors 26 are propelled throughthe system by the center conveyor 18.

Assuming movement to be in a left to right direction, contact of theends of the shafts 32, 34 upon the support rails 68 causes rotation ofthe rotors 26 in a clockwise direction. If the motor also drives thebelt assemblies of the contact belt unit 124 in a clockwise direction,the direction of rotation of the rotors 26 will reverse uponencountering the lower flight of element 166 at the entrance of the unit124 (the relationship at contact being as depicted in FIG. 9). Suchcontact causes a significant proportion of the powder on the outercircumferential surface of the cylindrical core portion 28 of the rotors26 to be displaced therefrom and to fall into the powder recovery hopper184, which is positioned at an appropriate location beneath the deck 36(as may be seen in FIG. 3); most, if not all powder entering the slots30 as a result of such contact will simply fall out during subsequentrotation of the rotor 26. The hopper 184 is connected to the powderrecovery and feed unit through a vacuum system (not illustrated) by aconduit 186. Most of the remaining powder on the surface of the coreportion 28 is picked up by the contact element 166 of the belt assembly,as previously described, with any additional powder being removed by thesuccessive belt cleaning effects in the same manner. As will beappreciated, since the rotors 26 are supported for free rotation, aftercontact with the contact element 166 they turn at precisely the samespeed under the influence thereof. This prevents relative wiping orbrushing action between the element 166 and the rotors 26, such as wouldtend to cause uneven deposits to be produced, particularly at the edgesof the slots 30 where complete coverage is most important.Notwithstanding the backup blocks 165, pressure from the belt assemblieswill generally be attributable only to the weight thereof. Nevertheless,the contact element 166 would tend to enter the slots 30 as a result ofrelative movement, wiping and removing powder from the edges thereof.Accordingly, the substantial absence of such movement constitutes aprimary benefit of the present invention. The nozzles 170 and associatedvacuum conduits 172 are adjustably supported in the bifurcated endportions of the nozzle support arms 168 with the nozzles 170 lyingclosely adjacent the contact elements 166. In this way, the powderpicked up by the elements 166 is withdrawn from the cells thereof and isconveyed to the recovery portions of the system for recycle.

Positioned within the powder removal zone near the forward end of thesecond belt assembly of the unit 124 is a pair of vacuum blocks 188,which are secured to the deck Ji) along the sides of the travel path. Ascan best be seen in FIG. 12, each of these blocks has a face plate 190,190' secured upon its upper surface and of an elongated vacuum channel192 extending lengthwise therein. As can be seen with additionalreference to FIGS. 3 and 13, a vacuum nozzle 194 of generally oval crosssection is secured against the lower surface of each of the vacuumblocks 188, each nozzle 194 having a circular throat portion 196 aboutwhich is positioned an annular mounting collar 200 by which it issecured against the associated vacuum block 188 (by means not shown).Secured over the throat portion 196 of each nozzle 194 is a vacuum hose198 which is connected to a vacuum source (not shown) and ultimately tothe powder recovery and feed unit illustrated in FIGS. 1 and 2.

The fact plates 190, 190' on the vacuum blocks 188 are provided withelongated slots 202, 202, each of which extends in a generally angularrelationship outwardly from the travel path. These slots 202, 202register over the channels 192 in the blocks 188 and serve to define aflow passage for air under the influence of vacuum drawn through theconduits 198. As the armature rotors 26 travel between the vacuum blocks188 with the shafts 32, 34 thereof in rolling contact upon the faceplates 190, 190 respectively, the vacuum effect from below thoroughlycleans the shafts 32, 34 of any powder which may have become depositedthereon. Normally, powder will be present in the shafts 32, 34 as aresult of the initial electrostatic coating operation and/or due todisplacement from the circumference of the cylindrical core portion 28during powder removal by the first belt assembly in the contact beltunit 124. The divergent disposition of the slots 202, 202 will causeparticles of powder to be removed first from the portions of the shafts32, 34 adjacent the core portion 28 and progressively outwardlytherealong. It will be appreciated that the nonlinear and nonuniformconfiguration of the slot 202 is necessitated by the configuration ofthe crank shaft 34 which passes thereover. As can be seen in FIGS. 9 and10, a hold-down bracket 201 is secured to each of the vacuum blocks 188.Each bracket 201 includes a pressure plate element 203 which overliesthe slot 202, 202' of the associated block 188 and serves to engage thetops of the shafts 32, 34 as they are conveyed thereunder, therebyforcing the shafts against the face plates 190, 190' to ensure efficientpowder removal therefrom.

After travelling past the vacuum blocks 188, the armature cores 26 areconveyed beneath the third of the series of belt-cleaning assemblieswhile being supported upon parallel side rails 182. The forth contactbelt effect is similar in design to the first three, with the exceptionthat it is provided with contact belt assemblies for the shafts 32, 34as well as for the cylindrical core portion 28 of the rotors 26. Theconstruction of this portion of the contact belt unit 124 is mostclearly illustrated in FIG. 11, wherein it can be seen that a set ofthree belt pulleys 154 are mounted on a common shaft for simultaneousrotation. Each of the pulleys has a belt assembly consisting of asupport belt 164 and a contact belt 166 constructed as hereinbeforedescribed, and it will be appreciated that the belts extend between twoof such sets of three belt pulleys 154 (as can be seen in FIG. 10). Theouter belt assemblies are cleaned by passage under nozzles of the vacuumassembly 171, shown only in FIG. 3. It should be appreciated thelocation of the belt assemblies for the shafts may be altered from thatillustrated; for example, relocating them to the second of the four belteffects may facilitate operation of the vacuum blocks 188 thereat andrender shaft cleaning more effective.

From the contact belt unit 124, the armature rotors 26 pass into aprecuring unit, generally designated by the numeral 204 and shown inFIGS. 3 and 14. With specific reference to the latter figure, it can beseen that the precuring unit 204 consists of a cover assembly, generallydesignated by the numeral 206, which has affixed thereto a pair of anglebrackets 208, only one of which is visible in FIG. 14. The brackets 208are secured at one end to the cover assembly 206 by appropriate bolts210, and the opposite ends thereof are pivotally supported upon posts212 which are mounted upon the deck 36 of the machine. Also secured tothe cover assembly 206 is a right angle contact arm 214 which has anelement extending over the end of a spring-loaded plunger assembly 216.In normal operation the cover assembly 206 will be maintained in theposition illustrated in full line in FIG. 14 by fluid pressure meansacting against the upward force of the plunger assembly 216. If themachine stops or if some emergency situation occurs, the fluid pressureforce is disrupted, permitting the plunger assembly 216 to immediatelyraise the cover assembly 206 to the position shown in phantom line.

The cover 218 of the cover assembly 206 is elongated (as can be seen inFIG. 3) and is of inverted, generally U-shaped configuration (as isshown in FIG. 14). It has a number of layers 220 of insulating materiallining the top wall thereof, which are secured, along with a metal sheetreflector 222 and a pair of elongated angular baffle plates 224, to thecover 218 by appropriate bolts 226. Heating elements 228, which may beCALROD units, extend longitudinally within the cover 218 and aresupported therein by a number of inserts 230, which are spaced along thelength of the cover 218 and have pairs of apertures 231 to receive andsupport the heating elements 228. The baffle plates 224 are constructedwith inclined walls 232 which slope downwardly and inwardly toward oneanother and toward the travel path; the walls serve to support theinserts 230 as well as their primary function of reflecting andconcentrating heat from the elements 228 upon the central portion of thetravel path.

Supported along each side of the cover 218 at the lower edges thereof isone of a pair of configured cooling blocks 234, which may be constructedof aluminum or another suitable material having a high heat transfercoefficient. It will be appreciated that these cooling blocks areelongated and extend along substantially the entire length of the cover218. The cooling blocks 234 have inner upstanding elements 235 which areconfigured to define behind them circular recesses 236, in which aresupported cooling tube portions 238. Small, downwardly opening U-shapedchannels 240 are defined along the lower inner edges of the upstandingelements 235, and a depending ridge 242 is provided on each of thecooling blocks 234 adjacent the lower outer edge thereof.

The ridges 242 of the cooling blocks 234 are received in narrow,upwardly opening U-shaped channels 244 defined in the upper surface ofthe base of the precuring unit 204, the base being generally designatedby the numeral 246. A relatively large, upwardly opening U- shapedchannel 250 extends axially in the base 246 along its entire length todefine the travel path there through. The underside of the base 246 hasa U-shaped channel 248 of a similar size running along its length, withthe opposed relationship of the channels creating a relatively thinfloor portion 252 therebetween. A rectangular base block 254 is seatedin the downwardly opening channel 248 and is welded in place with itsupper surface spaced a short distance downwardly from the lower surfaceof the floor portion 252 to define a shallow water channel 256therebetween. Upwardly opening U-shaped slots 258 are formed in theupper surface of the block and along the entire length thereof betweenthe central channel 250 and each of the relatively narrow channels 244,and each of the slots 258 has a cover strip 260 engaged over its openend to thereby define closed conduits therewithin.

At each end (only one end being shown) the base 246 is provided with atransverse bore 262 which communicates with the opposite ends of theshallow water channel 256. To facilitate manufacture, the bores 262 aresimply drilled inwardly from the side of the base 246, with plugs 264being inserted afterward to close the ends. Extending upwardly andinwardly from the opposite ends of the bores 262 are short connectingchannels 266 (only two of the four of which are seen because only oneend of the base 246 is illustrated), one of which communicates with eachof the U-shaped slots 258 at one end thereof. Finally, an inlet port 268communicates from the lower surface of the base 246 with the transversebore 262, and it will be appreciated that the other end of the base 246has a similar port 268 communicating with the associated bore 262provided thereat.

In operation, the precure unit 204 heats the cylindrical core portion 28of each of the armature rotors 26 while simultaneously cooling theshafts 32, 34 thereof.

' Heat is generated by the elements 228, with the reflector 222 and thebaffle plates 224 effectively directing the heat inwardly toward thecore portion 28 and concentrating it thereat. The simultaneous coolingeffect is provided by passing water through the base 246 and theconfigured cooling blocks 234. With respect to the base 246, waterpasses inwardly through the illustrated port 268, transversely acrossthe block in the bore 262, and thence along the length of the base 246within the shallow water channel 256 and the U-shaped slots 258 to passoutwardly through the transverse bore and port not illustrated. In thismanner, a cooling effect is transmitted through the thin floor portion252 to cool the central band 176 of the conveyor 18 and the surroundingarea. Water passing through the slots 258 serves not only to cool thesides of the conveyor 18, but has the primary function of producing acooling effect through the cover strips 260. The shafts 32, 34 of thearmature rotors 26 contact these strips 260 directly, so that thecooling water passing therebeneath very effectively lowers thetemperature of those portions. The configured blocks 234 are cooled bywater passing into one of the cooling tube portions 28 and out of theother, the portions 238 being parts of a continuous conduit. As aresult, the horizontal part 237 of each of the blocks 234 is cooled andcooperates with the base 246 to effectively maintain the shafts 32, 34at a relatively low temperature. The upper ends of the carrier tabs 178,178 of the conveyor 18 extend into the downwardly opening U-shapedchannels 240 adjacent the lower inner edges of the blocks 234, and arecooled thereby. In addition, the engagement of the depending ridges 242in the upwardly opening channels 244 increases the effectiveness ofcooling by unifying the cover 218 and base 246 of the precure unit 204.A low temperature shell is thereby defined about the travel path throughthe precuring unit 204, except in the limited area thereabove at whichthe heating effect is concentrated. Accordingly, the unit 204 veryeffectively cools parts of the rotors 26 which lie outwardly of thecylindrical core portion 28, while the portion 28 is heated to arelatively elevated temperature. As a result, only resin on the coreportion 28 is melted and fused, with any powder remaining on the shafts32, 34 being maintained in a solid particulate state. This permitsremoval of unwanted powder from the shafts 32, 34 while simultaneouslyproducing a relatively adherent coating in the slots of the core portion28, the circumferential surface of the core portion 28 having been freefrom powder by the action of the belt assemblies in the contact beltunit 124.

Turning now in detail to FIG. 15, therein illustrated is an air knifeassembly, generally designated by the numeral 270, which is positionedimmediately downstream from the precurc unit 204, as can be seen in FIG.3. The air knife assembly 270 consists of a pair of spaced, invertedU-shape bridge members 272 which have mounted thereon a pair of spacedair manifold bars 274. The manifold bars 274 are adjustable (by meansnot shown) to vary their spacing and angular attitude relative to oneanother, and each of them has a number of flattened nozzles or airknives 276 extending downwardly therefrom toward the deck 36 of themachine. In general alignment under each of the manifold bars 274 is anupwardly opening elongated trough 278 which is connected to a vacuumsource (not shown) through vacuum conduits 280 attached to the lowerends thereof. As will be readily appreciated, armature rotors 26 passfrom the precuring unit 204 beneath the bridge members 272 of the airknife assembly 270 with their shafts 32, 34 extending outwardly over thetroughs 278. Air is charged under pressure into the manifold bars 274through the air conduits 282 and is blown at high velocity upon theshafts 32, 34 through the air knives 276 as the rotors 26 travel throughthe assembly 270. Due to the discrete form in which the particles aremaintained as a result from the cooling ef fects of the precuring unit204, the air from the knives 276 effectively dislodges any particlespresent on the shafts 32, 34 and propels them into the troughs 278. Inthis manner, the shafts are thoroughly cleaned prior to entry of therotor 26 into the oven, with the excess powder being returned to thesystem through the conduits 280. As will now be appreciated, uncoatedarmature rotors 26 are loaded in successive pairs of slots 52, 52' ofthe conveyor bands 44, 45 at the infeed station of the apparatus, andenter the oven with at least partially fused and cohered coatings ofresin in the slots 30 and on the end faces 37 thereof. Thecircumferential surfaces of the cylindrical core portions 28 of therotors 26 are virtually devoid of any powder particles. This isaccomplished by the contact belt elements 166, which effectively removeall powder deposited thereon without causing significant amounts of theresin to be removed or built up at the edges of the slots 30, which isachieved due to the absence of any significant wiping or brushingeffect.

The sh .fts 32, 34 are preliminarily cleaned in the belt contact unitE24 by passage over the slotted face plates 190, 190 of the vacuumblocks 188, and by the contact elements 166 of the fourth set of beltassemblies, as illustrated in FIG. 11. Thereafter, the rotors 26 pass tothe precuring unit 204 at which the powder remaining on selectedportions may be partially fused and cohered (when a thermoplastic resinis used) so as to permit other portions to be finally cleaned withoutdisturbing the desired deposits. While it should be appreciated that theprecuring unit 204 might be eliminated if so desired, and might beinappropriate under certain circumstances, preferred practice utilizes athermoplastic resin and both the contact belt unit 124 and the precuringunit 204, as illustrated. From the precuring unit 204 the rotors 26 arecarried to the air knife assembly 270 for a final cleaning, through theoven for complete fusion, and finally to the cooling unit forsolidification of the resin.

Subsequent to the air knife assembly 270 and ahead of the oven is asecond transfer point which occurs over the rearmost drive sprocket 13.Since the transfer is quite comparable to that which occurs over thesprocket 12, a detailed explanation is not believed to be necessary.However, as illustrated in FIG. 16, the construction of the conveyor 20to which the cores are transferred at this point is somewhat differentfrom any described previously. More particularly, the conveyor 20consists of a pair of spaced chain assemblies, generally described bythe numeral 283 (only one being shown in FIG. 16) which, at the point oftransfer, lie to either side of the conveyor 18. Each of the chainassemblies 283 includes an endless sprocket chain 292 on which ismounted a multiplicity of U-shaped cradles 284. Each of the cradles 284has in its inner wall 288 an upwardly opening U-shaped socket 286 inwhich the shafts of the rotors are received. The cradles 284 have adepending flange element 290 secured thereto, and the flange elementsconstitute part of the sprocket chain 292 while affording the means ofattachment thereto. As will also be appreciated, drive sprocket 13 willconsist of a pair of sprocket wheels similar to those employed for thedrive sprocket 12, one wheel being used to support and drive each of thechain assemblies 283.

Of the numerous types of materials which are suitable for use as theparticulate resin, thermoplastics, and particularly syntheticthermoplastic resins, are preferred. Exemplary of such thermoplasticresins are the vinylidenes and vinyls (e.g., polystyrene and polyvinylchloride), the olefins (e.g., polyethylene, polypropylene and copolymersthereof), the cellulosics, polyamides (e.g., nylons), etc. Generally,the resin will be a powder smaller than mesh (i.e., substantially all ofthe particles will pass through an 80 mesh (U.S.) sieve. Preferably, thepowder will be less than mesh, and most desirably it will be mesh orfiner.

As will be' appreciated by those skilled in the art, many changes may bemade in the illustrated apparatus without departing from the concept ofthe invention hereof. For example, heating (when used) may be by anyappropriate means, and may employ convection, conduction, infrared,induction, or like effects. Similarly, cooling may be accomplished inany appropriate manner, such as by the use of cooled air of other fluid,conventional refrigeration, etc. The proper electrical circuitry willalso be readily apparent and of the type conventionally employed in theelectrostatic coating and electromechanical arts. It should beappreciated that, although good practice and safe operating procedureswill normally dictate electrical grounding of the apparatus and of theworkpiece by contact therewith, no special provision need normally bemade for grounding of the workpiece to ensure adequate electrostaticattraction and adhesion. The high voltage charging of the particles willusually suffice to establish an adequate potential relative to theworkpiece, regardless of the measures taken with respect to the latter;however, independent connections may be made to the workpiece if sodesired.

Although the term fusion as used herein will most generally relate tothe effect induced at elevated temperatures, as is consistent with itsmost literal definition, a somewhat broader interpretation is intendedto be applied to its present use. Thus, for example, treatment withsolvent vapors and electron irradiation can be used to induce flow incertain materials, and in instances in which materials of those typesare employed the term fusion is intended to encompass such techniques.Moreover, ultrasonic vibrations may be utilized to produce fusion ofcertain types of particles. As will be apparent, in such cases suitableequipment will be used instead of the oven depicted in the drawing; itwill also be apparent that such techniques will permit other materialsto be employed for the coating, for example materials which are notwell-suited to use at elevated temperatures. The terms partial fusionand coherence are intended to connote a state in which the individualparticles of the resin have been affected by the fusion treatmentsufficiently to at least loosely join them together, so as to resistseparation. In such a condition individual particles may be discernible,whereas upon complete fusion or melting the particles are no longeridentifiable as such. Due to the variety of resinous materials that maybe employed in the practice of the invention, it is not possible toplace specific values upon the temperatures or other conditions involvedfor fusion or melting without unduly limiting the scope hereof.Moreover, the conditions of operation that are appropriate in suchinstance will be readily apparent to those skilled in the art in view ofthe foregoing detailed information.

Thus it can be seen that the present invention provides a novel methodand apparatus for the production of a coating of a solid, particulateresin upon a limited portion of a workpiece. More specifically, itprovides such a method and apparatus for electrostatically coating theworkpiece and for effecting the removal of the resinous material fromselected portions thereof which are to be uncoated, and the method andapparatus are particularly adapted for coating reentrant surfaceportions of generally cylindrical articles. The coatings are producedquickly, easily and economically, and on an automatic and continuousbasis if so desired. A novel contact belt unit is also provided which isadapted to remove the particulate resin from one portion or zone of aworkpiece without causing undue thinning or thickening of the deposit onan adjacent portion thereof.

Having thus described the invention, 1 claim:

1. A method for the production of a coating of resinous material upononly a portion of a workpiece, comprising the steps of:

a. producing a cloud of electrostatically charged solid particles ofresinous material;

b. exposing said workpiece to said charged particles with said workpiececharged effectively opposite thereto to cause a layer of particles todeposit thereon;

c. thereafter, contacting a particle-coated portion of said workpiecewith a relatively resiliently deformable contact surface having a smallopen-cell construction, under conditions avoiding relative move mentbetween elements of said workpiece portion and of said contact surfacewhile in such contact, thereby lodging particles from said coatedportion in the cells of said contact surface while avoiding substantialwiping action between said contact surface and said workpiece portion;and

d. thereafter, separating said contact surface and said workpiece withsaid particles lodged within the cells of said contact surface tothereby effect the removal of particles from said contacted portion.

2. The method of claim 1 wherein said workpiece is moved along a travelpath during such contact with said contact surface, and wherein saidcontact surface is simultaneously moved adjacent thereto.

3. The method of claim 2 wherein said workpiece is a cylindrical articlesupported for free rotation reentrant its axis transversely across saidtravel path, and wherein contact by said contact surface is on acircumferential surface thereof and causes rotation of said article withsaid circumferential surface thereof moving at the same linear speed asthat at which said contact surface moves.

4. The method of claim 3 wherein said article is an armature rotor foran electric machine having reen-' trant surface portions in thecylindrical core portion thereof defining winding slots therein, andwherein said contact element removes particles from the circumferentialsurface of said core portion without causing undue thinning orthickening of said layer of particles along the edges of said slots.

5. The method of claim ll wherein said contact surface is comprised ofan open-cell foam elastomer having a cell size of about 1 to 20 mils,and wherein said resinous material is a powder consisting essentially ofparticles smaller than about mesh.

6. The method of claim 1 wherein said resinous material is fusible, andwherein said method includes the additional step of treating saidparticles of resinous material remaining on said workpiece subsequent tosaid particle removal step to cause at least partial fusion andcoherence thereof.

7. The method of claim 6 wherein said resinous material isthermoplastic, and wherein said treating step is one of heating saidparticles to a temperature above ambient.

* k =l-' i

1. A METHOD FOR THE PRODUCTION OF A COATING OF RESINOUS MATERIAL UPONONLY A PORTION OF A WORKPIECE, COMPRISING THE STEPS OF: A. PRODUCING ACLOUD OF ELECTROSTATICALLY CHARGED SOLID PARTICLES OF RESINOUS MATERIAL;B. EXPOSING SAID WORKPIECE TO SAID CHARGED PARTICLES WITH SAID WORKPIECECHARGED EFFECTIVELY OPPOSITE THERETO TO CAUSE A LAYER OF PARTICLES TODEPOSIT THEREON; C. THEREAFTER, CONTACTING A PARTICLE-COATED PORTION OFSAID WORKPIECE WITH A RELATIVELY RESILIENTLY DEFORMABLE CONTACT SURFACEHAVING A SMALL OPEN-CELL CONSTRUCTION, UNDER CONDITIONS AVOIDINGRELATIVE MOVEMENT BETWEEN ELEMENTS OF SAID WORKPIECE PORTION AND OF SAIDCONTACT SURFACE WHILE IN SUCH CONTACT, THEREBY LODGING PARTICLES FROMSAID COATED PORTION IN THE CELLS OF SAID CONTACT SURFACE WHILE AVOIDINGSUBSTANTIAL WIPING ACTION BETWEEN SAID CONTACT SURFACE AND SAIDWORKPIECE PORTION; AND D. THEREAFTER, SEPARATING SAID CONTACT SURFACEAND SAID WORKPIECE WITH SAID PARTICLES LODGED WITHIN THE CELLS OF SAIDCONTACT SURFACE TO THEREBY EFFECT THE REMOVAL OF PARTICLES FROM SAIDCONTACTED PORTION.
 2. The method of claim 1 wherein said workpiece ismoved along a travel path during such contact with said contact surface,and wherein said contact surface is simultaneously moved adjacentthereto.
 3. The method of claim 2 wherein said workpiece is acylindrical article supported for free rotation reentrant its axistransversely across said travel path, and wherein contact by saidcontact surface is on a circumferential surface thereof and causesrotation of said article with said circumferential surface thereofmoving at the same linear speed as that at which said contact surfacemoves.
 4. The method of claim 3 wherein said article is an armaturerotor for an electric machine having reentrant surface portions in thecylindrical core portion thereof defining winding slots therein, andwherein said contact element removes particles from the circumferentialsurface of said core portion without causing undue thinning orthickening of said layer of particles along the edges of said slots. 5.The method of claim 1 wherein said contact surface is comprised of anopen-cell foam elastomer having a cell size of about 1 to 20 mils, andwherein said resinous material is a powder consisting essentially ofparticles smaller than about 80 mesh.
 6. The method of claim 1 whereinsaid resinous material is fusible, and wherein said method includes theadditional step of treating said particles of resinous materialremaining on said workpiece subsequent to said particle removal step tocause at least partial fusion and coherence thereof.
 7. The method ofclaim 6 wherein said resinous material is thermoplastic, and whereinsaid treating step is one of heating said particles to a temperatureabove ambient.